Three attacks, including one by a suicide bomber disguised as a churchgoer, targeted three churches in Indonesia's second largest city of Surabaya on Sunday.
At least three people were killed and 10 others wounded, police and media reported.
The first attack at the Santa Maria Roman Catholic church killed two people, including the suspected bomber, and wounded 11, police spokesman Frans Barung Mangera told TVOne network.
It was followed by a second explosion in a different church that killed another person. Two were rushed to hospital.
Three more people were wounded in a third attack, Mangera said.
The latest attacks in predominantly Muslim Indonesia came days after police ended a riot and hostage-taking at a detention centre near Jakarta that left five dead and five injured. The Islamic State group has claimed responsibility.
Indonesia has carried out a sustained crackdown on militants since bombings by al-Qaida-affiliated radicals in Bali in 2002 killed 202 people.